Clean up shared sync locks on close/pagehide

[longfellowone]

Follow-up to #811

Summary

• Abort pending db-lock requests on worker-wrapped close to avoid hanging lock waits.
• Make worker-wrapped cleanup idempotent and notify close listeners.
• Ensure shared sync pagehide triggers close-signal cleanup for tab-close locks.

Tests

• pnpm --filter @powersync/web run build:tsc
• pnpm vitest --run tests/force_close_db_lock_abort.test.ts tests/shared_sync_db_lock_cleanup.test.ts tests/shared_sync_pagehide.test.ts
• pnpm build:packages
• pnpm vitest

[changeset-bot]

🦋 Changeset detected

Latest commit: 50e5fab

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

Name	Type
@powersync/web	Patch
@powersync/diagnostics-app	Patch

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